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International Journal of Heat and Mass Transfer, Volume 56, Issues 1–2, 1 January 2013, Pages 350-359.
Y.S. Lim, S.C.M. Yu, N.T. Nguyen
Division of Aerospace Engineering, School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore
Division of Thermal and Fluid Engineering, School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore
Abstract
Flow visualization of gas–liquid two-phase flows in circular glass tubes with inner diameter of 500 and 300 um have been conducted. The 300 um tube is further utilized for the investigation of the heat transfer characteristics under constant heat flux at wall. The constant heat flux is supplied by joule heating via applied electric current through a thin uniform indium tin oxide coating. To ensure steady flow patterns, the two-phase flow is achieved by injecting nitrogen gas coaxially through a centrally positioned tube to the continuous liquid phase flow. Measurements of wall temperature along the heating zone, various flow patterns and pressure drop are recorded simultaneously. Thermal performance is found to depend on bubble size, void fraction, Reynolds number and flow patterns. The two-phase Nusselt number (NuG,L) for bubbly flow is found to increase by 176% compared to the single phase flow, while the corresponding pressure drop increases by less than 27%.
